1. Field of the Disclosure
The present disclosure relates to measuring a parameter of motion of a tool in a borehole and, in particular, to determining the parameter of axial motion from an angle of rotation of a freely-rotating member of a tool conveyed in the borehole.
2. Description of the Related Art
Petroleum exploration generally involves drilling a borehole into a formation or reservoir using a drill string with a drill bit at a bottom end of the drill string. The borehole may be a vertical borehole drilled to a selected depth or, in some cases, an inclined or horizontally drilled borehole within the reservoir. In order to construct a borehole to the selected depth, it is necessary to determine a distance and/or distance-related parameters within the borehole. Such distance parameters may include, for example, measured depth, rate of penetration, build-up rate, hole curvature, etc. Current methods of measured depth determination are using surface measurements, such as those involving a combination of cumulative pipe lengths and a top drive position. The wellbore geometry then is calculated from the hole direction at several certain depth, as measured downhole, which may include gravitometers and magnetometers. Using these methods, the measured depth and the wellbore geometry is derived on surface rather than downhole. Alternatively, gyroscopes may be used the measure three-dimensional movement and hence position. These measurements each include an amount of error both in their measurements and the processing of their measurements to obtain parameters of motion. The methods disclosed herein provide a method of determining a parameter of axial motion by correlating a rotation of a member of the drill string with distance traveled in the borehole.